As the use of digital communications has increased over the past few decades, engineers have been faced with the challenge of building receivers that are of a practical size and reasonable cost. While driven in the past to reduce size and cost, a large portion of the marketplace was composed of users--such as the military--that required small to moderate quantities of a particular receiver model. In addition, requirements for substantial capability/functionality and extreme environmental/reliability characteristics resulted in receivers that were large and bulky: albeit they were virtually "bulletproof". The marketplace has now changed and a large part of the user community is composed of the commercial sector. As such, the requirements placed on communication equipment have also changed with increased pressure to meet price points acceptable for high volume product markets. Within this market, simpler receivers with very focused functionality, low power consumption, and reduced size are desired, and the object of the invention is to provide receivers meeting this criteria.
The receiver disclosed herein is called the Integrated Receiver (IR.) The name reflects both its inherent nature for overlapping several receiver processes within a common processing path and its amenability for implementation using highly integrated circuitry. The IR's operating advantages stem from its unique signal processing characteristics that are achieved through novel use of charge coupled devices (CCD) technology and integrated tracking loop techniques.
CCD technology has been used for many years. Probably, its most notable application has been in the camera industry. However, recent advances in CCD design and fabrication have led designers to consider new uses for this technology. For example, see Weinberg et al. U.S. Pat. No. 5,126,682, which relates to a demodulation system incorporating CCD devices, which is incorporated herein by reference. The present invention is directed to receivers for communication, sonar and radar applications.
The CCD is a combination of analog and digital circuitry whose properties exploit the best from both worlds. Its analog input matches well with signals provided by receiver front-ends and the device is capable of directly producing a digital output when integrated with an A/D converter. Furthermore, the device may be controlled and clocked digitally thereby providing a natural interface with a system processor. When configured as a transversal filter (see U.S. Pat. No. 5,126,682), the CCD offers several key features including:
Wide input dynamic range. PA0 Variable clocking speeds. PA0 Variable/fixed tap weights. PA0 Multibit tap weights. PA0 Large number of stages. PA0 Length control. PA0 Auxiliary processing functions. PA0 Filter, PA0 Demodulate, PA0 Store samples, PA0 Decimate, PA0 Despread, PA0 Tune, PA0 Amplify/Attenuate,
Given the features noted above, the CCD becomes an extremely useful device for receivers as disclosed herein. Through its proper use, the device can:
incoming signals. The IR according to this invention exploits the CCD's features so as to simplify digital signal processing requirements within the receiver.